Method of producing pyridine

ABSTRACT

A method of producing pyridine, comprising vapor-phase oxidation of 2-picoline with oxygen at a temperature of 300*-380* C on oxide vanadium-titanium catalysts at a molar ratio of vanadium pentoxide to titanium dioxide of 1:0.5-16. The process of oxidation is carried out at a molar ratio of 2picoline to oxygen, ammonia and water equal to 1:10-60:1-10:40100 respectively. The resulting oxidation products are entrapped by dissolving them in water. The aqueous ammonia solution of the reaction products is subjected to heat treatment at a temperature of 250*-300* C and a molar ratio of ammonia to said reaction products of at least 0.5 mole of ammonia per mole of the said products, pyridine being thus obtained. The present method makes it possible to produce pyridine with a yield of up to 87-97 percent as calculated for the 2-picoline used and up to 90-99 percent as calculated for the 2-picoline reacted.

United States Patent Suvorov et al.

[151 3,689,491 [451 Sept. 5, 1972 [54] METHOD OF PRODUCING PYRIDINE [72] Inventors: Boris V. Suyorov, ulitsa Pushkina, 10 2/44, kv. 27; Alfred Davydovich Kagarlitsky, ulitsa Timiryazeva, 71, kv. 44; Iskra lvanovm Kan, ulitsa Masanchi, 76, kv. 68; Olga Borisovna Lebedeva, 3 mikroraion, 31, kv. 17, all of Alma-Ate, U.S.S.R.

[22] Filed: June 7,1971

[21] Appl.No.: 150,792

[52] US. Cl. ..260/29() R, 260/294.9, 260/295 R,

, 260/290 P [51] Int. Cl. ..C07d 31/12 [58] Field of Search ..260/290, 294.9, 295

[56] References Cited UNITED STATES PATENTS 2,845,428 7/1958 Wettstein ..260/295 Primary Examiner-Henry R. Jiles Assistant Examiner- Harry I. Moatz Attorney-Waters, Roditi, Schwartz & Nissen 57 ABSTRACT A method of producing pyridine, comprising vaporphase oxidation of 2-picoline with oxygen at a temperature of 300380 C on oxide vanadium-titanium catalysts at a molar ratio of vanadium pcntoxide to titanium dioxide of 1:05-16.

The present method makes it possible to produce pyridine with a yield of up to 87-97 percent as-calculated for the Z-picoline used and up to 90-99 percent as calculated for the 2-picoline reacted.-

1 Claim, N0 Drawings METHOD OF PRODUCING PYRIDINE The present invention relates to methods of producing pyridine which finds wide application in chemical industry and in the production of pharmaceuticals.

Known in the art is a method of producing pyridine by vapor-phase oxidation of 2-picoline with oxygen over an oxide vanadium-molybdenum catalyst applied onto a nickel-aluminum alloy, in the presence of water vapors.

Considerable quantities of pyridine are also known to be forming in case of vapor-phase oxidation of 2- picoline with oxygen in the presenceof ammonia and water vapors at a temperature of 360 C, with the molar ratio of Z-picoline to oxygen, ammonia and water equal to l:l.8:3.4 respectively, over an oxide vanadiumchromium catalyst on an aluminum oxide carrier.

The disadvantage of the known methods is that they ensure a relatively low yield of the desired product which does not exceed 66.5 percent of the theoretical amount as calculated for the 2-picoline used.

The object of the present invention is to provide a method of producing pyridine which would ensure a higher yield of the desired product.

In accordance with said and other objects the invention consists in carrying out vapor-phase oxidation of 2- picoline in the presence of ammonia and water vapors on mixed vanadium catalysts at a temperature ranging from 300 to 380 C. As said catalysts use is made of oxide vanadium-titanium catalysts with the molar ratio of vanadium pentoxide to titanium dioxide of 1:05-16. The process of oxidation is run with 2-picoline, oxygen, ammonia and water being taken in a molar ratio of 1:10-60:1-10z40-100 respectively. The resulting oxidation reaction products which are a mixture of pyridine, and Z-pyridinecarboxamide or a mixture of said compounds with an ammonium salt of 2- pyridinecarboxylic acid are entrapped by dissolving them in water. The aqueous ammonia solution of the reaction products is subjected to heat treatment at a temperature of 250-300 C and a molar ratio of ammonia to said reaction products of at least 0.5 mole of ammonia per mole of the said products. As a result of the heat treatment, the ammonium salt of 2- pyridinecarboxylic acid is decarboxylated with the formation of pyridine, and 2 cyanopyridine and 2- pyridinecarboxamide are subjected to hydrolysis to the ammonium salt of Z-pyridinecarboxylic acid, the latter salt being then decarboxylated to pyridine.

The addition of ammonia and water vapors into the oxidation reaction zone contributes to suppression of deep oxidation processes that are accompanied by the destruction of the pyridine ring to such low-molecular compounds as CO, CO, and HCN, while favoring the formation of such products of incomplete oxidation as the ammonium salt of Z-pyridinecarboxylic acid, 2- pyridinecarboxarnide, Z-cyan-pyridine and pyridine.

The above-specified ratios between 2-pi'coline, oxygen, ammonia and water make it possible to increase the yield of the incomplete oxidation products with the preserved structure of the pyridine ring up to 90-98 percent.

The running of the oxidation process in the presence of ammonia in such a manner as to ensure a predominant formation of the reaction products with the preserved structure of the pyridine ring and efiecting pyridine the processes of hydrolysis and decarboxylation to convert nitrogen-containing derivatives of 2-pyridinecarboxylic acid to pyridine result in the yield of pyridine increased to 87-97 percent as calculated for the 2- picoline used and to 90-**percent as calculated for the 2-picoline reacted.

The herein-proposed method of producing pyridine is efiected as follows.

A vapor-gas mixture of 2-picoline, molecular oxygen or air, ammonia and water is passed through a throughflow reactor filled with a catalyst whose grains are 3 to 5 mm in size. The rate of feeding the initial 2-picoline, oxygen or air, ammonia and water should be such that the molar ratio of the 2-picoline to the oxygen, ammonia and water would be equal to 1:1 60:1 10:40 respectively. The temperature of the oxidation reaction is varied to lie within 300 to 380 C with the time of contact from 0.1 to 1 second. In case the oxidation process is run under milder conditions, that is, at lower temperatures and shorter time of contact, there form such products of incomplete oxidation of 2- picoline as pyridine, Z-cyanopyridine, Z-pyridinecarboxarnide and an ammonium salt of 2-pyridinecarboxylic acid. In case the conditions of running the oxidation process are more stringent, that is, the temperatures selected are more elevated and the time of contact is longer, there form all the above-said products with the exception of the ammonium salt of 2- pyridinecarboxylic acid.

Upon leaving the reactor, the vapor-gas mixture of the reaction products is taken to a scrubber sprayed with cold water. The products of incomplete oxidation of 2-picoline with the preserved structure of the pyridine ring are entrapped by being dissolved in water.

The aqueous-ammonia catalyzate and contact gases (C0, C0,, HCN) are analyzed by using gas chromatography and polarography techniques.

The aqueous-ammonia solution (catalyzate) containing Z-cyanopyridine and Z-pyridinecarboxamide or said products in a mixture with an ammonium salt of 2- pyridinecarboxamide acid, 250- is subjected to heat treatment in a'steel autoclave or a tubular furnace at a temperature of 250-300C during l-3 hours. The

molar ratio of ammonia to the nitrogen-containing derivatives of Z-pyridinecarboxylic acid should be at least 0.5 mole of ammonia per mole of said products. In case the amount of ammonia proves to be less than required, the necessary quantity thereof is added to the solution in the form of a 25 percent solution of NI-LOH. In the course of the heat treatment of the aqueous-ammonia solution the ammonium salt of Z-pyridinecarboxylic acid is decarboxylated with the formation of v and 2-pyridinecarboxamide and 2- cyanopyridine are hydrolyzed with subsequent decarboxylation to pyridine.

For a better understanding of the present invention,

the herein-proposed method of producing pyridine is illustrated by the following examples.

EXAMPLE 1 Contact oxidation of 2-picoline is carried out in a through-flow reactor equipped with one reaction tube dioxide taken in a molar ratio of 120.5. A vapor-gas mixture of Z-picoline, water, ammonia and air is passed through the reaction tube which is heated to 300 C. The components are fed at the following rate: 2- picoline, l g/hr; ammonia, 7.3 g/hr; air, 650 l/hr; water, 78 g/hr. The time of contact is 0.3 seconds. The experiment lasts for hours. The reaction products are entrapped in scrubbers sprayed with cold water. On

completion of the experiment the contents of the scrubbers are analyzed by using gas chromatography and polarography techniques. Found in the catalyzate: 19.7 (23.5 percent) of pyridine, 66.6 g (59.5 percent) of 2-cyanopyridine, 3.3 g (7.5 percent) of 2- pyridinecarboxamide, 9.8 g (2.5 percent) of 2- pyridinecarboxylic acid and 0.6 g (6 percent) of 2- picoline.

The aqueous ammonia solution of said compounds is subjected to heat treatment in a steel autoclave. The amount of the catalyzate per charge is 50 ml. At a temperature of 250 C the experiment lasts for 3 hours. After the extraction of the reaction liquid with chloroform and rectification thereof 77.5 g of pyridine are isolated (boiling point, 115 C; n 1.500), which amounts to 87.0 percent as calculated for the 2- picoline fed and to 92.5 percent as calculated for the 2- picoline reacted.

EXAMPLE 2 The reaction of contact oxidation of 2-picoline is carried out in the equipment as described in Example isolated, this being 87.3 percent as calculated for the 2- picoline fed and 95.6 percent as calculated for the 2- picoline reacted.

EXAMPLE 3 The reaction of contact oxidation of 2-picoline is carried out in the apparatus described in Example 1. The catalyst is a mixture of vanadium pentoxide and titanium dioxide taken in a molar ratio of 1:16. The rate of feed of 2-picoline is 5.5 g/hr; water, ammonia and oxygen (air oxygen) are taken in a ratio of -100, 1-10 and 10-60 moles per mole of 2-picoline respectively. The reaction temperature is varied within 330 to 380 C, the time of contact is within 0.13 to 0.75 seconds.

The reaction products are entrapped and analyzed as described in Example 1.

The heat treatment of the catalyzate is efi'ected on a continuous-action installation which is a tubular furnace, the tube thereof being 8,600 mm long and 12 mm in diameter. With the reaction temperature of 250 C the experiment lasts for 3 hours, at 270 C it lasts for. 2 hours and at 300 C, for hour.

Pyridine is isolated from the reaction liquid by salting out with potash with subsequent rectification.

The conditions of oxidizing 2-picoline, composition of the oxidation products and yield of pyridine after the heat treatment of the nitrogen-containing derivatives of Z-pyridinecarboxylic acid are given in the following table.

TABLE Yield of pyridine after heat Conditions of contact oxidation of 2-picoline Composition of oxidation products of Z-picoline (in percent) treatment 01 in the presence of ammonia as calculated for the Z-picoline fed catalyzate As cal- As cal- Deep culated culated Molar ratio of l-pyl'l- 2-pyrioxidation for the 2- for the 2- Z-picoline, oxy- Time 01 dinecardineear- (products picoline picolino Reaction temgen, ammonia contact, 2-p 1coboxylic box- Z-cyano- O+CO used, reacted, perature, C. and water sec. line acid amide pyridine Pyridine +HCN) percent percent 1:36:45: 0.53 2.5 3.0 6.0 47.5 41.0 96.0 98.5 1210222100 0.70 3.0 3.0 9.0 16.0 65.0 2. 0 95. 5 98. 5 1:36:4z45 0. 34 6. 0 2. 5 5. 5 42. 5 41. 0 2. 0 U0. 5 96. 1255:1260 0.25 3.5 2.5 5.0 61.5 27.5 95.1 08. 1:60:1z50 0.28 3.0 4.0 8.0 54.0 24.5 6.0 89.0 92. 1255:4255 0. 39 7. 0 2. 0 4. 0 45. 0 36. 6 0. 5 90. 5 97. 1260:8240 0.39 1. 5 3.0 8. 0 50.0 37. 0 0. 3 95. 5 08. l 220: 10:45 0. 2" 2. 0 2. 5 10.0 50. 3 25. 2 1. 0 96. 2 98. 1:1522z60 0. 34 1. 6 2. 5 8.8 52. 5 32. 5 2. 1 94.0 J4. 121624. 5:100 0.48 3.0 2. 0 6. 6 37. 0 47.0 2. 5 91. 2 95. 1:36:4z40 0.58 2.0 1.5 3.6 45.0 43.0 3.0 91.5 04. 1;15:4.5290 0.58 4.0 40.2 50.0 5.0 93.0 93. 115526180 0.39 2.0 8.0 45.0 43.0 2.0 96.9 96.

1. The catalyst 18 a mixture of vanadium nentoxide and What IS claimed is:

titanium dioxide taken in a molar ratio of 1:8. The reaction temperature is 360 C. The rate of feed is as follows: 2-picoline, 7.85 g/hr; ammonia, 1.8 l/hr; air, 300 l/hr; water, 74.5 g/hr. The time of contact is 0.6 seconds. The experiment lasts for 10 hours. The reaction products are entrapped and analyzed as described in Example 1. Found in the catalyzate: 21.5 g (36.0 percent) of pyridine, 42.4 g (48.0 percent) of 2- cyanopyridine, 5.1 g (5.0 percent) of Z-pyridinecarboxamide and 6.28 g (8.0 percent) of 2-picoline.

After adding 10 ml of a 25 percent solution of ammonia to the catalyzate, the latter is subjected to heat treatment in the apparatus described in Example 1. The temperature of the reaction is 260 C and its duration is 2.5 hours.

After azeotropic distillation and rectification 57.6 g of pyridine (boiling point, 1 14 5 C; r1 1.505) are l. A method of producing pyridine, comprising vapor-phase oxidation of 2-picoline with oxygen at a temperature of 300-380 C on oxide vanadium-titanium catalysts at a molar ratio of vanadium pentoxide to titanium dioxide of l:0.5-16 in the presence of ammonia and water vapors at a molar ratio of 2-picoline to oxygen, ammonia and water equal to 1:10 60:1 10:40 respectively; entrapment of the resulting oxidation products which are mixtures of compounds selected from the group consisting of a mixture of pyridine, 2-cyanopyridine and 2-pyridinecarboxamide and a mixture of pyridine, Z-cyanopyridine, 2- pyridinecarbox amide and an ammonium salt of 2- pyridinecarboxylic acid, by dissolving said oxidation reaction products in water; subjecting the aqueous-ammonia solution of the reaction products to heat treatment at a temperature of 250-300 C and at a molar cyanopyridine and Z-pyridinecarboxamide being hydrolyzed to the ammonium salt of Z-pyridinecarboxylic acid with subsequent decarboxylation of said salt to pyridine. 

